Founded late in 1926 to bid for the Chicago-San Francisco section of the transcontinental mail
route,Boeing Air Transport won the contract, starting services in July 1927 with new
aircraft produced by its owners,
the Boeing Airplane Company. From the beginning Boeing also
carried passengers.

In January 1928, Boeing bought one of the early mail carriers, Pacific Air Transport, flying
between Seattle and Los Angeles.
Pacific continued as a separate division, also after United
Aircraft & Transport Corporation was created
by Boeing Airplane Co. as a holding company in
February 1929. Among the United companies were also the aircraft builders
Sikorsky and Stearman,
as was the engine producer Pratt & Whitney. The Boeing System (as the operating airlines
of the United group became known) was augmented with further acquisitions, in June 1929 of
Stout Air Lines,
and during mid-1930 of Varney Air Lines, flying mail
between Seattle and Salt Lake City, and of NAT - National Air Transport.
NAT held the important mail contract between New York and Chicago and was merged with the Stout
division, enabling the Boeing System to offer a complete transcontinental mail and passenger
service.

During the spring of 1931, the Boeing System became known as the United Air Lines, from July
1931
also the new name of the holding company. After the cancellation of the mail contracts in
1934,United Air Lines was reorganized as an operating company, merging
all the divisions.